Hwa-Il Seo

A very large integrated pH-ISFET sensor array chip compatible with standard CMOS processes

Abstract The development and preliminary evaluation of a very large pH-sensitive ISFET sensor array chip is reported in this paper. The sensor array chip boasts a 15×16 array of pH-ISFETs with on-chip control and readout circuits. It was designed and fabricated using a novel process which is compatible with standard CMOS technology. This process only required four new mask layers in the design stage and four extra standard processing steps in the fabrication stage. A novel signal processing technique was also employed.

ISFET glucose sensor based on a new principle using the electrolysis of hydrogen peroxide

Abstract An ISFET glucose sensor based on a new principle using the electrolysis of hydrogen peroxide, one of the by-products of the oxidation of glucose, and a Pt electrode actuator is proposed and the characteristics investigated. Compared with the conventional ISFET glucose sensor, the proposed sensor shows an improvement of four times the sensitivity, an extension of the dynamic range to 5 mM glucose concentration, and a faster response of 3 min in 10 mM phosphate buffer solution (pH 7.4, 100 mM NaCl). In addition, the baseline of the sensor response can also be checked, so that the influences of drift of the ISFET and pH change in the sample solution can be eliminated. The sensor shows a large dependence on the buffer concentration. When the buffer concentration is changed from 5 to 20 mM, the sensitivity decreases by a factor of four. However, the high sensitivity, 9 mV mM 1 even in 20 mM buffer concentration, will still allow the sensor to measure glucose concentrations of human blood without the need for dilution.

All solid type ISFET glucose sensor with fast response and high sensitivity characteristics

Abstract An all solid type ISFET glucose sensor using the electrolysis of hydrogen peroxide has been fabricated and the characteristics investigated. By forming thin-film type three electrodes on the ISFET chip for amperometric actuation, miniaturized solid-type sensor could be achieved. The sensor with a specially designed ladder-type working electrode showed improved operation in response time and response magnitude.

Chemical HF Treatment for Rear Surface Passivation of Crystalline Silicon Solar Cells

P-type Si wafers were dipped in HF solution. The minority carrier lifetime (lifetime) increased after HF treatment due to the hydrogen termination effect. To investigate the film passivation effect, PECVD was used to deposit SiN x on both HF-treated and untreated wafers. SiNx generally helped to improve the lifetime. A thermal process at 850℃ reduced the lifetime of all wafers because of the dehydrogenation at high temperature. However, the HF-treated wafers showed better lifetime than untreated wafers. PERCs both passivated and not passivated by HF treatment were fabricated on the rear side, and their characteristics were measured. The short-circuit current density and the open-circuit voltage were improved due to the effectively increased lifetime by HF treatment.

Miniaturized ISFET glucose sensor including a new structure actuation system

A new principle of an amperometric actuation technique was incorporated in the ISFET glucose sensor. The ISFET is fabricated by the CMOS process and the platinum working electrode is deposited by the lift-off process. A sensor with a specially designed ladder type working electrode exhibits improved operation in response time, response magnitude and detection range. An expectation concerning the reduction of sensor size is also discussed.

Improved automatic gain control circuit using fuzzy logic

A problem that arises in most communication receivers concerns the wide variation in power level of the signals received at the antenna. These variations cause serious problems which are usually be solved in receiver design by using Automatic Gain Control (AGC). AGC is achieved by using an amplifier whose gain can be controlled by using external current or voltage. We have to note that the AGC circuit does not respond to rapid changes in the amplitude of input and multifrequency. Nowadays, with the development of the fuzzy theory, the advantages of the fuzzy logic are recognized widely and deeply. Applying fuzzy logic to AGC circuit is a way to enhance AGC circuit.

A Study on High Frequency-Plasma Enhanced Chemical Vapor Deposition Silicon Nitride Films for Crystalline Silicon Solar Cells

SiNx:H films have been widely used for anti-reflection coatings and passivation for crystalline silicon solar cells. In this study, SiNx:H films were deposited using high frequency (13.56 MHz) direct plasma enhanced chemical vapor deposition, and the optical and passivation properties were investigated. The radio frequency power, the spacing between the showerhead and wafer, the ratio, the total gas flow, and the gas flow were changed over certain ranges for the film deposition. The thickness uniformity, the refractive index, and the minority carrier lifetime were then measured in order to study the properties of the film. The optimal deposition conditions for application to crystalline Si solar cells are determined from the results of this study.

Interaction of Di-Methylaluminum Groups with Hydroxyl Groups on a Fully Hydroxyl-Terminated Si (001) Surface

The interaction of - with -OH on a fully OH-terminated Si (001) surface was studied using density functional theory. Two sites for to react with the -OH on the surface were identified. The product energetically favored the dimer-row site rather than the inter-row site because the Al atom of at the dimer-row site was attracted by the lone pair electrons of the O atom in the neighboring -OH. The energy barrier for the transfer of the between the two sites was 0.11 eV, and therefore, the at the inter-row site can easily transfer to the dimer-row site at room temperature.

Indium Nanowire Growth on Si (001) Surface Using Density Functional Theory

Density functional theory was utilized to investigate the growth of an indium nanowire on a Si (001) buckled surface. A site between the edge of two Si dimers is most favorable when the first In atom is adsorbed on the surface at an adsorption energy level of 2.26 eV. The energy barriers for migration from other sites to the most favorable site are low. When the second In atom is adsorbed next to the first In atom to form an In dimer perpendicular to the Si dimer row, the adsorption energy is the highest among all adsorption sites. The third In atom prefers either of the sites next to the In dimer along the In dimer direction. The fourth In atom exhibited the same tendency showed by the second atom. The second and fourth In adsorption energy levels are higher than the first and third levels as the In atoms consume the third valence electron by forming In dimers. Therefore, the In nanowire grows perpendicular to the Si dimer row on the Si (001) surface, as it satisfies the bonding of the three valence electrons of the In atoms.

Structural Study of Tetragonal-Ni1-xPdxSi/Si (001) Using Density Functional Theory (DFT)

Tetragonal-Ni Pd Si/Si (001) structure was studied by using density functional theory (DFT). An epitaxial interface between 2 × 2× 4 (001) tetragonal-NiSi supercell and 1 × 1× 2 (001) Si supercell was first constructed by adjusting the lattice parameters of B2-NiSi structure to match those of the Si structure. We chose Ni atoms as a terminating layer of the B2-NiSi; the equilibrium gap between the tetragonal-NiSi and Si was calculated to be 1.1 A. The Ni atoms in the structure moved away from the original positions along the z-direction in a systematic way during the energy minimization. Two different Ni sites were identified at the interface and the bulk, respectively. The two Ni sites at the interface have 6 and 7 coordination numbers. The Ni sites with coordination number 6 at the interface were located farther away from the interface, and were more favorable for Pd substitution.